1. Field of the Invention
This invention relates to a sealing assembly for a rotating member. More particularly, this invention relates to a dynamic seal assembly for apparatus having a rotary shaft and containing a particulate product.
2. Description of the Prior Art
Although this invention will, for sake of clarity and brevity, be described in respect of a drying drum for polyethylene powder, it is not so limited. This invention is applicable to other types of apparatus that operate in a similar manner.
A conventional polyethylene powder drying drum has a large, hollow drum body pierced longitudinally at its opposing ends with a hollow shaft. The drum is fixed and the shaft turns within the drum. The shaft carries a torus disk rotor for conveying powder in the interior of the drum from one opposing end of the drum to the other, and in so doing drying (separating) the powder (polyethylene particles) from its carrier fluid (hexane).
The hexane wet powder is inserted into the interior of the drum at one end thereof, moved by the torus disk rotor through the longitudinal length of the drum to the opposing end thereof, and dried powder removed from the interior of the drum at that opposing end.
The shaft carrying the torus disk rotor extends out of each of the opposed ends of the drum and rotates in order to turn the torus disk rotor. For polyethylene drying the shaft turns at about 10 revolutions per minute. The shaft is hollow in order for steam to pass through its interior thereby providing drying heat to the interior of the drum and the wet powder. Outside the drum, and close by either opposed end of the drum, the shaft carries a bearing assembly for supporting the rotating shaft.
The polyethylene powder being dried in this apparatus is quite fine, from about 0.5 to about 200 microns. Preventing this powder from seeping out of the drum at the points where the turning shaft extends through the opposing ends of the drum is problematic.
Heretofore, a seal has been used that employs a packing gland with a mating follower, a recess in the gland containing no less than five Teflon based packing rings, and what is known as a lantern ring that is made of Teflon. These packing rings are made of braided rope, and, therefore, are fibrous in nature. All these packing rings are formed from a length of braided packing rope, and are wrapped around the shaft they are to seal against. This can be seen in greater detail by reference to FIG. 2 herein.
These prior art packing rings do not compact evenly when put under pressure by tightening of the packing gland follower for sealing purposes. The packing rings closer to the follower compacted significantly, while the rings further removed from the follower did not compact as much, if at all. These rings tended to leak powder when they became worn. More significantly, leakage occurred when the shaft inevitably wobbled to some, even slight, degree. This was due to the rings not always following the shaft back as it resumed its original position after the wobbling stopped. However it occurred, the leakage resulted in the release of powder from the interior of the drum to the surrounding atmosphere in an uncontrolled and undesired manner.
Also, this prior art seal assembly, with its multitudinous fibrous packing rings, required so much follower tightening for sealing purposes that the rings generated sufficient heat from friction with the shaft that powder that contacted the seal assembly was melted to some degree. This melted powder created a tenacious deposit inside the drum that was difficult, at best, to remove, and added time loss and expense to the routine maintenance of the drying apparatus. This melted powder, in time, gradually destroyed the packing rings causing increased leakage of powder from within the drum to outside the drum.
Further, due to the shaft supporting bearing assemblies that are carried outside and close to each end of the drum, it was quite difficult and expensive to replace the prior art seal assemblies with new assemblies of the same type. This also added time loss and expense to the maintenance of the drying apparatus.
Accordingly, this type of drying apparatus cried out for a more effective seal assembly that produced less frictional heat, and could be removed and replaced in a timely manner without undergoing the expense of removing the bearing assemblies that supported the shaft outside the opposed ends of the drum.
This invention solves all these problems at the same time. This invention provides a dynamic seal that maintains its seal when the shaft wobbles by moving with the shaft, and does so with less frictional heating of the seal assembly. The seal of this invention does not depend on tightening of the follower for sealing purposes, and can be removed from the shaft and a new seal of the same type mounted on the shaft without touching the bearing assemblies that support that shaft.